The field of the disclosure relates generally to gas turbine engines and, more particularly, to a method and system for controlling a clearance gap between fan blade tips and a metal fan casing using fan casing heating.
In at least some known aircraft engines, a fan casing fabricated from a composite material surrounds a fan including a plurality of fan blades. A clearance gap necessarily exists between tips of the fan blades and the fan casing, to avoid rub of the blade tips against the fan casing. Because composite materials are much less susceptible to thermal growth, the diameter of these composite fan casings is defined to accommodate the maximum diameter (from base to tip) of the fan blades while still maintaining a clearance gap between the blade tips and the fan casing. Accordingly, the blade tips expand to their maximum diameter during takeoff, which restricts the minimum diameter of the fan casing. However, the fan casing remains at substantially this same minimum diameter during all other flight phases, including cruise, at which the diameter of the fan blades is reduced relative to the maximum fan blade diameter experienced during takeoff. As a result, the clearance gap, or the difference between the diameter of the fan blades and the diameter of the fan casing, during cruise is much larger than is necessary, which reduces the efficiency of the fan and, therefore, reduces the performance of the engine.